It is known that a block copolymer can be obtained by an anionic copolymerization of a conjugated diene compound and an alkenyl arene compound by using an organic alkali metal initiator. Block copolymers have been produced which comprise primarily those having a general structure
A--B and A--B--A
wherein the polymer blocks A comprise thermoplastic polymer blocks of alkenyl arenes such as polystyrene, while block B is a polymer block of a selectively hydrogenated conjugated diene. The proportion of the thermoplastic blocks to the elastomeric polymer block and the relative molecular weights of each of these blocks is balanced to obtain a rubber having unique performance characteristics. When the content of the alkenyl arene Compound is small, the produced block copolymer is a so-called thermoplastic rubber. In such a rubber, the blocks A are thermodynamically incompatible with the blocks B resulting in a rubber consisting of two phases; a continuous elastomeric phase (blocks B) and a basically discontinuous hard, glass-like plastic phase (blocks A) called domains.
While in general these block copolymers have a number of outstanding technical advantages, one of their principal limitations lies in their sensitivity to oxidation. This behavior is due to the unsaturation present in the elastomeric section comprising the polymeric diene block. Oxidation may be minimized by selectively hydrogenating the copolymer in the diene block, for example, as disclosed in U.S. Pat. No. 27,145.
These selectively hydrogenated block copolymers are further deficient in many applications in which interactions are required between it and other materials. Applications in which improvements in adhesion characteristics may promote improved performance include 1) the toughening of, and dispersion in, polar polymers such as the engineering thermoplastics; 2) the adhesion to high energy substrates in a hydrogenated block copolymer elastomer based high temperature adhesive, sealant or coating material; and 3) the use of hydrogenated elastomers in reinforced polymer systems. The placement of functional groups onto the block copolymer provides interactions not possible with hydrocarbon polymers and, hence, extends the range of applicability of this material.
U.S. patent application Ser. No. 07/198,543 now abandoned, teaches that substantial improvement in the high temperature capabilities of the block copolymer can be obtained by the addition of sulfonic acid functional groups to the arene blocks, A, without substantially modifying the elastomeric B blocks. The high-temperature properties are improved by reacting the block copolymers with an acyl sulfate to add sulfonic acid functional groups in an all acid form. The sulfonic acid groups can be partially neutralized or totally neutralized with metal ions to form metal sulfonate salts. The acid and salt forms of the sulfonated block copolymers achieve excellant high temperature properties with a loss in processability. The processability of non-modified block copolymers is frequently improved by the addition of aliphatic hydrocarbon extender resins. However, typical aliphatic hydrocarbon resins have not been used with selectively sulfonated block copolymers and the effect on polymer properties could not be predicted.